One type of idling speed-up control apparatus has been hitherto disclosed in Japanese Unexamined Patent Application Sho No. 58-206847. A load detecting means is provided for detecting the value of an electric load connected to an electric generator which is driven by an engine. A means is provided for setting a control value according to the detected value of the electric load. Also provided is a means for adjusting the air intake amount of the engine basing on this control value, so that an idling speed-up control is proportional to the value of the electric load.
Additional types of idling speed-up control apparatuses have been hitherto disclosed in Japanese Unexamined Patent Application Publications Sho No. 59-103932 or Sho No. 59-103945. An idling speed-up means is provided for stepwise increasing an idling speed of an engine, so that the idling speed-up means operates when the detected value of an electric load, detected by a load detecting means, is above a predetermined value. Thus, the idling speed-up control is an on-off type of control.
The prior art examples are inconvenient because adjusting means for an amount of air intake or control systems of the devices become complicated and are expensive. Of the foregoing prior art examples, the on-off control type of idling speed control is more advantageous than the former example in terms of cost.
However, with the on-off control type of idling speed control, one problem that arises is due to hunting. To prevent this problem from occurring, one arrangement causes an idling speed-up control means to continuously operate when the detected value of the electric load remains above a pre-determined value for a predetermined length of waiting time. Thus, the idling speed-up means is prevented from operating during a momentary increase of the electric load.
However, usually in this case, the waiting time is fixed for the same length of time regardless of the value of the electric load. Accordingly, if the waiting time is set to be comparatively long, the engine speed becomes much lower during the high load before the idling speed-up means is actually operated. The result is an unpleasant vibration and an engine stall. If the waiting time is set to be comparatively short, the engine speed is increased prematurely during a low load. The engine is thus inclined to race, which can often result in a lower fuel economy. Thus, conventional idling speed-up apparatus have had a difficult problem to be equally effective during both a high load and a low load.